Countershaft driving system for internal combustion engine and the like



Nov. 12, 1963 G. P. HANLEY 3, 10,195

COUNTERSHAFT DRIVING SYSTEM FOR INTERNAL COMBUSTION ENGINE AND THE LIKE Filed Dec. 27, 1961 IN VEN TOR. BY 4 Wfiazzig 14 7' TOR/VIE) United States Patent COUNTERSHAFT DRIVING SYSTEM FOR IN'I'ER- NAL COMBUSTION ENGINE AND THE LIKE George P. Hanley, Northville, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Dec. 27, 1961, Ser. No. 162,533 2 Claims. (Cl. 74-604) This invention relates generally to a countershaft driving system; more particularly to a countershaft driving system wherein at least one of the shafts is operably connected to sequentially drive one or more associated load devices spaced longitudinally thereof; and with regard to certain of its more specified aspects, to a counterrotating cam and balance shaft driving arrangement for an internal combustion engine.

The invention is herein shown and described for illustrative purposes as applied to a relatively high speed twocycle unifiow scavenged internal combustion engine generally of the type shown and described in the United States Patent No. 2,179,709 to A. F. Brecht, entitled Internal Combustion Engine; in United States patent application S.N. 1,488 entitled Internal Combustion Engine filed January 11, 1960, in the names of Harold H. Albinison et al.; and in copending United States patent application S.N. 34,728 filed June 8, 1960, in the names of George W. Conover et al. Such engines are characterized by use of overhead unit fuel injectors and uniflow scavenged exhaust valves sequentially operated by counterrotating cam and balance shafts which are synchronous- 1y driven in phased relation to the engine crankshaft and have eccentric balancing masses thereon adapted to counteract the primary rocking couples generated by and acting on the engine.

The sequential high speed operation of the several valves and unit fuel injectors in engines of the type indicated subject their actuating camshaft to a repetitive series of transverse eccentrically applied shock or impact type loads which produce fatigue inducing high speed stress reversals therein. In time, such high speed stress reversals may result in fatigue failure of the camshaft, particularly if the camshaft has some minor metallurgical, machining or heat treating flaw not detectable by normal preassembly inspection methods. This camshaft fatiguing problem is further aggravated or extended by the modern tendency to design smaller, lighter, more compact engine packages for a given output. To provide the desired power output, these smaller engines are generally rated at higher continuous and intermittent maximum speeds. The high fuel injection pressures necessarily required for adequate injection and more eflicient combustion under such operating conditions tend to impose still further critical stress reversals on the camshafts of such engines. This is also true in uprating the speed and power of existing engines by turbocharging, increasing the effective compression ratio, etc. Within the dimensional limits imposed by the particular engine design, fatiguing of the camshaft may be partially alleviated by changes in the camshaft material, configuration and/ or heat treatment.

The high speed load reversals applied to or acting on the camshafts of engines of the type indicated are also transmitted or referred back to the camshaft driving gears. This causes lash and destructive impact chattering to occur between the interengaged gear teeth with eventual gear tooth fatigue failures. This lash and chattering condition may be further aggravated by the use of counterrotating engine balancing masses mounted on or associated with the cam and balance shaft driving gears.

In the illustrative embodiment, the invention contemplates and features means for drivingly interconnectice ing and torsionally prestressing the counterrotating cam and balance shafts of an engine thereby damping and minimizing extreme stress changes and eliminating fatigue inducing high speed cyclic load and stress reversals within the cam and balance shafts and maintaining the several shaft driving gears in continuous lash free driving engagement.

The foregoing and other objects, advantages and features of the invention will be apparent from the follow ing description of an illustrative embodiment, having reference to the accompanying drawings, in which:

FIGURE 1 is a somewhat diagrammatic elevational view of a two-cycle internal combustion engine of the type indicated with portions thereof broken away and showing the illustrative environment of the invention; and

FIGURE 2 is a diagrammatic perspective view showing the cam and balance shaft driving arrangement of the invention as applied to the balance and timing system of the two-cycle internal combustion engine of FIG- URE 1.

Referring more particularly to FIGURE 1, a two-cycle uniflow, scavenged V-type internal combustion engine is indicated generally by the reference numeral 10. This engine is similar to that shown and described in the above mentioned S.N. 1,488 application. Two spaced parallel galleries 12 and 14 extend longitudinally through the engine cylinder block or frame member 16. Cam and balance shafts 18 or 213 are rotatably mounted within the galleries 12 and 14, respectively, by a plurality of longitudinally spaced bearings, the end bearings being shown at 22, 24, 26 and 28.

A combined gear and balance weight member 32 is drivingly secured to the rear end of the camshaft 20 and is counterdriven by a second combined gear and balance weight member 42 similarly secured on the rear end of the camshaft 18. The gears 32 and 42 each have an eccentric engine balancing mass formed integrally therewith as indicated at 34 and 44, respectively. These eccentric masses are oriented as shown in mounting the gears 32 and 42 on their respective camshafts and cooperate in their counterrotation to negate the primary rocking couple normally acting upon or applied to the rear of the engine. The gear 42 is driven through an idler gear 46 by a timing gear 48 mounted on the rear of the engine crankshaft 50.

In accordance with the invention, a third combined gear and eccentric balance weight member 52 is secured to the forward end of the camshaft 18 and rotatably driven therewith. The gear 52 drivingly engages a fourth gear and balance weight member 62 secured to the forward end of the camshaft. The gears 52 and 62 are preferably interchangeable with the gears 32 and 42 but as shown are so mounted on their respective camshafts as to orient the eccentricity of the engine balancing masses 54 and 64 diametrically opposite those of the gears 32 and 42. The counterrotating engine balancing masses 54 and 64 thus cooperate to negate the primary rocking couple acting on the front of the engine.

The several timing gears 32, 42, 52 and 62 are preferably provided with helical gear teeth. When oriented as shown, such gears serve to balance the thrust reactions applied to their respective cam and balance shafts. The gear securing keyways of the camshafts are 'angularly disposed so as to require torsional preloading of each shaft prior to or during assembly of the paired gears on at least one end thereof. The helical gear tooth interengagement and axial movement effected in mounting such keyed gears on the ends of their respective shafts cooperate to impart a limited torsional twist to each shaft. If additional shaft preloading is required or where straight gear teeth are used, the rear ends of the cam a and balance shafts 18 and 20 are first restrained from rotation by interengagement of their driving gears and by use of other appropriate means. Either one or both of the cam and balance shafts 18 land 26 are then rotated or twisted at their forward ends by appropriate means to torsionally prestress one or both of the Camshafts, as the case may be. Where both camshafts are prestressed in assembly, such prestressing is maintained by inferengagement of the gears 52 and 62 upon being drivingly secured to the forward ends of the respective cam and balance shafts. This is accomplished prior to removing the shaft rotating means. Where only one shaft is torsional-1y prestressed, the gears are similarly secured to the forward ends of the respective shafts in driving in-terengagement. Upon release of the initially prestressed shaft from the shaft rotating or twisting means, however, the torsional prestr-ess initially applied to the one shaft is divided or distributed between the two shafts.

The torsional loading or prestressing thus effected during assembly maintains the several gears 32, 42, 52 and 62 in continuous lash free driving interengagement and serves to damp and otherwise minimize the stresses induced by the'sequential shock load cam actuation of the several valve and injector mechanisms and completely eliminates fatigue inducing high speed cyclic stress reversals within the cam and balance shafts.

While the invention has been shown and described for illustrative purposes as applied to a V-type internal combustion engine of the type indicated, it will be apparent that it is equally applicable to any engine having similar counterrotating cam and balance shafts and auxiliary engine balance weights. The invention is also applicable in its broader aspects to other similar countershaft load driving systems. Hence, various modifications and changes might be made from the illustrative embodiment without departing from the spirit and scope of the invention as defined in the following claims.

I claim:

1. In combination with an internal combustion engine subjected to reciprocating and rotational inertial unbalance, an engine vibration damping and balancing accessory drive system comprising,

a rotatably driven crankshaft,

a pair of cam and balance shafts journaled in parallel spaced relation to said crankshaft,

at least one of said shafts having a plurality of longitudinally spaced cams operable to sequentially actuate a plurality of valve and injector actuating mechanisms,

a first pair of interengaged gears drivingly mounted on adjacent ends of said cam and balance shafts to effect counterrotation therebetween,

said first gears each having an eccentric mass oriented and coacting to counterbalance a primary rocking couple acting on the adjacent end of the engine,

a second pair of interengaged gears drivingly mounted on the opposite adjacent ends of each cam and balance shaft,

said second gears each having an eccentric mass oriented and coacting to counterbalance a primary rocking couple acting on the adjacent other end of the engine,

gear means for drivingly connecting one of said first pair of gears to the engine driven crankshaft thereby driving said cam and balance shafts in synchronous phased relation thereto,

and said cam and balance shafts being torsionally loaded during gear assembly thereby prestressing said shafts, the torsional prestressing of said shafts damping and minimizing vibration and fatigue inducing high speed cyclic load and stress reversals normally imposed on said shafts and further maintaining the several gears in continuous lashwfree driving engagement.

2. In an internal combustion engine, a countershaft engine balancing and vibration damping accessory drive system comprising an engine driven crankshaft,

two shafts journaled in spaced parallel relation to said crankshaft, at least one of said shafts being operable to periodically actuate a plurality of accessory load devices spaced longitudinally thereof,

a first pair of gears drivingly secured to adjacent ends of said shafts and interengaged to elfect counterrotation therebetween,

gear means for drivingly connecting one of said first pair of gears to said driven crankshaft,

a second pair of gears drivingly secured to the ends of said shafts oppposite said first gears and interengaged during assembly to torsionally preload said shafts. thereby damping and minimizing fatigue inducing high speed cyclic load and stress reversals in said shafts and further maintaining the several gears in continuous lash-free driving engagement,

and said first and second pairs of gears each having an eccentric mass rotatable therewith and disposed in opposed phased relation on opposite ends of each shaft and phased to coact with the eccentric mass of the adjacent gear engaged therewith to damp reciprocating unbalance and rocking couples acting on said engine.

References Cited in the file of this patent UNITED STATES PATENTS 863,545 MacLachlan Aug. 13, 1907 2,333,122 Prescott Nov. 2, 1943 FOREIGN PATENTS 436,215 Italy June 4, 1948 684.101 Great Britain Dec. 10, 1952 

1. IN COMBINATION WITH AN INTERNAL COMBUSTION ENGINE SUBJECTED TO RECIPROCATING AND ROTATIONAL INERTIAL UNBALANCE, AN ENGINE VIBRATION DAMPING AND BALANCING ACCESSORY DRIVE SYSTEM COMPRISING, A ROTATABLY DRIVEN CRANKSHAFT, A PAIR OF CAM AND BALANCE SHAFTS JOURNALED IN PARALLEL SPACED RELATION TO SAID CRANKSHAFT, AT LEAST ONE OF SAID SHAFTS HAVING A PLURALITY OF LONGITUDINALLY SPACED CAMS OPERABLE TO SEQUENTIALLY ACTUATE A PLURALITY OF VALVE AND INJECTOR ACTUATING MECHANISMS, A FIRST PAIR OF INTERENGAGED GEARS DRIVINGLY MOUNTED ON ADJACENT ENDS OF SAID CAM AND BALANCE SHAFTS TO EFFECT COUNTERROTATION THEREBETWEEN, SAID FIRST GEARS EACH HAVING AN ECCENTRIC MASS ORIENTED AND COACTING TO COUNTERBALANCE A PRIMARY ROCKING COUPLE ACTING ON THE ADJACENT END OF THE ENGINE, A SECOND PAIR OF INTERENGAGED GEARS DRIVINGLY MOUNTED ON THE OPPOSITE ADJACENT ENDS OF EACH CAM AND BALANCE SHAFT, SAID SECOND GEARS EACH HAVING AN ECCENTRIC MASS ORIENTED AND COACTING TO COUNTERBALANCE A PRIMARY ROCKING COUPLE ACTING ON THE ADJACENT OTHER END OF THE ENGINE, GEAR MEANS FOR DRIVINGLY CONNECTING ONE OF SAID FIRST PAIR OF GEARS TO THE ENGINE DRIVEN CRANKSHAFT THEREBY DRIVING SAID CAM AND BALANCE SHAFTS IN SYNCHRONOUS PHASED RELATION THERETO, AND SAID CAM AND BALANCE SHAFTS BEING TORSIONALLY LOADED DURING GEAR ASSEMBLY THEREBY PRESTRESSING SAID SHAFTS, THE TORSIONAL PRESTRESSING OF SAID SHAFTS DAMPING AND MINIMIZING VIBRATION AND FATIGUE INDUCING HIGH SPEED CYCLIC LOAD AND STRESS REVERSALS NORMALLY IMPOSED ON SAID SHAFTS AND FURTHER MAINTAINING THE SEVERAL GEARS IN CONTINUOUS LASH-FREE DRIVING ENGAGEMENT. 